?-aminobutyric acid (GABAA) receptors are key sites of synaptic inhibition in the brain and are critical drug targets for therapeutic agents including benzodiazepines, barbiturates, general anesthetics and neurosteroids. Moreover compromised GABAA receptor function is central to a number of CMS pathologies including epilepsy, anxiety, sleep disorders, addiction, autism, mental retardation, depression and schizophrenia. Ubiquitination of lysine residues is a commonly used cellular mechanism to regulate both protein half-life and the endocytic fate. This accepted paradigm together with our preliminary studies has led us to formulate a central hypothesis driving the experiments described in this proposal: GABAA receptors are subject to direct ubiquitination of lysine residues with the intracellular domains of individual receptor subunits, a process that is subject to dynamic modulation by neuronal activity. Depending on the subunit ubiquitinated this covalent modification acts to decrease receptor half-life within the secretory pathway or enhances lysozomal targeting, thereby modulating GABAA receptor cell surface stability and the efficacy of synaptic inhibition. Our efforts will center on four complementary but distinct experimental goals: 1. To test the hypothesis that GABAA receptor [unreadable]3 subunit ubiquitination regulates receptor cell surface stability by modulating insertion at the plasma membrane 2. To test the hypothesis that GABAA receptor ?2 subunit ubiquitination regulates receptor cell surface stability by modulating lysozomal targeting 3. To test the hypothesis that ubiquitination modulates the efficacy of synaptic inhibition mediated by GABAA receptors 4. To test the hypothesis that neuronal activity regulates GABAA receptor cell surface stability by modulating receptor ubiquitination Together, our approaches will provide a more thorough understanding of the primary determinants that regulate accumulation of GABAA receptors at synaptic sites. The results of these studies will have the potential to make significant contributions to the development of novel therapeutic strategies for such debilitating disorders as epilepsy, anxiety, sleep disorders, addiction, autism, mental retardation, depression and schizophrenia.